Hang in there my friend
Though you bow in weariness
You are not alone
This is my third lavender bush over many years. They all up and die on me at some point. Though this is only a year old, I think that Sparky the squirrel has been digging around in the roots, burying nuts!
When I saw that all the green had gone, and my lavender plant looked shrivelled up and dead, I trimmed it back a little and added more potting soil.
After a short time I noticed new green growth. It looks like it may survive after all!